The invention relates to tungsten-halogen incandescent lamps and particularly those of the dual filament variety especially suited for use in vehicle headlights.
The invention also relates to methods of producing such lamps.
In tungsten-halogen lamps, the tungsten is normally evaporated from the filaments during operation and combines with the halogen to form a gaseous halide, which prevents the tungsten from depositing on the internal wall of the lamp's envelope. Upon returning to the tungsten filaments, the halide decomposes, resulting in the deposition of tungsten back onto the filaments and the release of additional halogen gas to assure continuation of the cycle. The halogen cycle is well known in the art and lamps employing it have been on the market for some time.
With particular regard to dual filament tungsten-halogen lamps such as those described in the aforementioned applications, it was heretofore considered necessary to subject each of the several, e.g., four, lead-in wires used in the lamp to a series of complex bending operations prior to securement of the wires within the press-sealed end of the lamp's envelope. These operations were deemed essential to assure proper orientation of the respective tungsten filaments which typically are secured to the ends of the lead-in wires which extend within the envelope. Understandably, errors during these bending operations can result in unacceptable variations in filament locations and accompanying rejection rates during manufacture. Additionally, because the four wires were positioned within the press sealed end in a planar relationship, a potential "bumping" problem existed whenever it was decided to further include wire support members within the envelope's press-sealed end. In the final headlight assembly, mounting rods are affixed to these support members to assure secured alignment of the lamp within the assembly. "Bumping" occurs when the end of the support members engage one or more of the positioned lead-in wires. Because placement of the wire support members typically occurs simultaneously with the press-sealing operations, "bumping" can cause misalignment of both the lead-in wires and the support members, in addition to electrical short-circuiting in the final assembly. There is also the possibility of an improper seal between these metal components and the respective glass envelope which may in turn adversely affect the operating characteristics of the final product.
It is believed, therefore, that an incandescent, dual filament tungsten-halogen lamp which obviates the aforedescribed disadvantages of known lamps, of this variety would constitute a significant advancement in the art.